Further evidence for the existence of an intrinsic bicarbonate-stimulated Mg2+-ATPase in brush border membranes isolated from rat kidney cortex

Abstract

The aim of this study was to provide further evidence for the existence of a nonmitochondrial becarbonate-stimulated Mg2+-ATPase in brush border membranes derived from rat kidney cortex. A plasma membrane fraction rich in brush border microvilli and a mitochondrial fraction were isolated by differential centrifugation. Both fractions contain a Mg2+-ATPase activity which can be stimulated by bicarbonate. The two Mg2+-ATPases are stimulated likewise by chloride, bicarbonate, and sulfite or inhibited by oligomycin and aurovertin, though to different degrees. In contrast to these similarities, only the Mg2+-ATPase activity of the mitochondrial fraction is inhibited by atractyloside, a substance which blocks an adenine nucleotide translocator in the inner mitochondrial membrane. On the other hand, filipin, an antibiotic that complexes with cholesterol in the membranes inhibits exclusively the Mg2+-ATPase of the cholesterol-rich brush border membranes. Furthermore it could be demonstrated by the use of bromotetramisole, an inhibitor of alkaline phosphatase activity, that the Mg2+-ATPase activity in the membrane fraction is not due to the presence of the highly active alkaline phosphatase in these membranes. These results support the assumption that an intrinsic bicarbonate-stimulated Mg2+-ATPase is present in rat kidney brush border membranes.

An azide‐insensitive low‐affinity ATPase stimulated by Ca2+ or Mg2+ in basal‐lateral and brush border membranes of kidney cortex

“…The relatively low HC0;-stimulation remaining in the presence of 5 mM azide can be explained by a lower percentage inhibition of mitochondrial ATPase by azide in the presence of activating anions [31]. Kinne-Saffran and Kinne [32] used atractyloside as an inhibitor. The insensitivity of HC0;-stimulated Mg'+-ATPase for this inhibitor in a rat kidney brush border membrane fraction, however, only proves the absence of intact mitochondria, but cannot exclude the presence of mitochondrial membrane fragments.…”

An ATP-driven proton pump in brush-border membranes from rat renal cortex

“…Since Skou described in 1957 the possible involvement of an ATPase in active sodium transport across biological membranes [40], an increasing number of ATPases has been speculated to act as ion pumps. Over the last years our interest has been focused on an anion-sensitive Mg 2 +-ATPase which could be proven to be present in brush-border membranes of the proximal tubule [25,26]. This ATPase has been tentatively hypothesized to be involved in proton transport.…”

Relation of ATPases in rat renal brush-border membranes to ATP-driven H+ secretion

“…The "Mg2+-ATPase '' measured in cortex homogenates [45], microdissected nephrons [32], and isolated brush-border membranes [5,20,31,44] is stimulated by Ca ~-+ and other nucleotides besides ATP [13,31,44,45], This pattern is typical for ecto-ATPases found in other cells [14,18,28,29,40,42] rather than for an ATPase involved in H + transport. The "bicarbonate-stimulated ATPase" in a rat kidney brush-border membrane preparation was related to ATP-driven H+se -cretion [35,36,41,43], but was later shown to be of mitochondrial origin [13,31,38]. Another candidate for H + secretion, the N,N'-dicyclohexylcarbodiimide (DCCD) and N-ethylmaleimide (NEM) sensitive ATPase was measured in microdissected and permeabilized proximal tubules [l], but a localization to the brush-border membrane was not demonstrated.…”